Communication network and method for transmitting data packets in the communication network

ABSTRACT

A communications network, computer program product and method for transmitting data packets in the communications network comprising synchronized nodes via a predetermined path in the communications network, wherein the synchronized nodes of the predetermined path include a source node, a target node and at least one intermediate node, the synchronized nodes synchronously feed data packets into the predetermined path and each have first and second buffers for respectively buffering high-priority data packets and low-priority data packets, wherein each intermediate node having an empty first buffer at a given point in time, and to which the source node feeds a high-priority data packet into the predetermined path toward the target node, generates a second high-priority data packet and feeds the generated second high-priority data packet into the predetermined path toward the target node so as to ensure high-priority data packets on the predetermined path are not delayed by low-priority data packets.

REFERENCE TO RELATED APPLICATIONS

This is a U.S. national stage of application No. PCT/EP2013/060285 filed17 May 2013. Priority is claimed on German Application No.DE102012210243.4 filed 18 Jun. 2012, the content of which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a communication network and method fortransmitting data packets in the communication network which comprisessynchronized nodes via a predetermined path in the communicationnetwork.

2. Description of the Related Art

Communication networks for control and regulatory processes, as in themanufacturing and processing industry, are often physically distributedsystems in which data need to be transmitted between the participatingnodes with a particular quality of service. Examples of such nodes arecontrollers, sensors, actuators or switches. The communication platformtypically used is an industrial Ethernet with realtime capability, suchas PROFINET. To ensure short end-to-end delays and little variationtherein, particularly jitter, the critical control and regulatory dataneed to be forwarded with preference, i.e., particularly with priority,over other data in the communication network.

The aforementioned PROFINET communication network as an example of anindustrial Ethernet standard is based on a time-division multiplexingmethod for ensuring different qualities of service. In this case, allthe nodes of the PROFINET communication network are synchronized to oneanother. A time cycle of the time-division multiplexing method usedcomprises fixed time windows for isochronous realtime traffic (IRT,Isochronous Realtime), other realtime traffic (RT, Realtime) and normaltraffic. This cycle is continually repeated. Within the respective timewindow, exclusively the traffic intended therefor is attended to. Otherpackets are buffer-stored at the respective node.

The time window for isochronous realtime traffic allows deterministictransfer characteristics, such as for motion control applications. Inthis context, the network resources along the scheduled path in thecommunication network are exclusively reserved even before the system isstarted up. Hence, there is a precise stipulation of when and on whatnetwork interface or port a node feeds in a packet or forwards areceived packet. This approach allows the prevention of competing accessto network resources, such as the simultaneous forwarding of packets viathe same port of a node. However, the available resources of thecommunication network cannot be jointly used by other trafficdynamically and hence efficiently.

In the time window for normal traffic, on the other hand, packets areforwarded based on their priority, particularly via strict priorityscheduling, and static multiplexing. Packets are forwarded only whenthey have been received completely. This can be called store and forwardforwarding. However, this can entail high-priority control andregulatory data packets experiencing waiting times at the nodes becausethe relevant port to which the packets are intended to be forwarded isalready blocked by an ongoing transmission process for another packet.This can result in greatly varying end-to-end delays. This problem isshown schematically in FIGS. 1 and 2. In this case, FIG. 1 illustrates aschematic diagram of a network topology for a communication network Nwith four nodes A, B, C, D. A path P of the communication network N isdetermined by the subpaths D-C, C-B and B-A. In addition, FIG. 2 shows aschematic diagram for the transmission of data packets P1-P3 via thecommunication network N of FIG. 1.

The packets P1 and P3 are high-priority data packets, whereas the packetP2 is a low-priority data packet. In this case, by way of example, thenode A is a control device (controller) to which high-priority datapackets, in this case the data packets P1 and P3, are transmittedcyclically from the sensor nodes B and D. By way of example, the node Cis an actuator that receives high-priority manipulated values cyclicallyfrom the control device A. Here, the node C sends only low-priority datapackets P2 to the node A. Furthermore, it can be assumed that thehigh-priority data packets P1 and P3 are transmitted as Ethernet packetshaving the same length. FIG. 2 considers exclusively the communicationin the direction of the node A, the destination node. However, acorresponding situation also applies to the opposite direction, in thatcase to the destination node D.

In detail, FIG. 2 shows the message flow diagram for the transmission ofthe data packets P1-P3 at the beginning of a cycle at the instant t=0.In this case, t shows the temporal extent, whereas R illustrates thespatial extent. At the instant t=0, the node B sends the high-prioritydata packet P1 in the direction of the node A, the node C sends thelow-priority data packet P2 in the direction of the node A and the nodeD sends the high-priority data packet P3 in the direction of the node A.Each node B, C, D has only one data packet P1, P2, P3 ready for sendingin the direction of the destination node A. As a result, the respectivedata packet P1, P2, P3 is transmitted at each node B, C, D. The problemis the long transmission period for the low-priority data packet P2 atthe node C on account of the high packet length thereof, particularly incomparison with the packet lengths of the high-priority data packets P1,P3.

At the node C, the high-priority data packet P3 arriving from theadjacent node D must wait for the complete transmission of thelow-priority data packet P2, since the transmission process for thelow-priority data packet P2 had already been started before the packetP3 arrived at the node C. Only after complete transmission of thelow-priority data packet P2 with the relatively high data length can thedata packet P3 be transmitted from the node C to the node B. At the nodeB, the data packet P3 must also then await the complete transmission ofthe data packet P2 from the node B to the node A. The result of this isa long delay for the high-priority data packet P3, particularly for longlinear topologies comprising a plurality of nodes.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide improvedtransmission of data packets in a communication network comprisingsynchronized data.

This and other objects and advantages are achieved in accordance withthe invention by providing a method for transmitting data packets in acommunication network comprising synchronized nodes via a predeterminedpath in the communication network is proposed. In this case, thesynchronized nodes of the predetermined path comprise a source node, adestination node and at least one intermediate node. The synchronizednodes feed data packets into the predetermined path in synchronized formand each have a first buffer store for buffer-storing high-priority datapackets and a second buffer store for buffer-storing low-priority datapackets. The method involves each of the intermediate nodes whose firstbuffer store is empty at a particular instant at which the source nodefeeds a first high-priority data packet into the predetermined path inthe direction of the destination node generating a second high-prioritydata packet and feeding the generated second high-priority data packetinto the predetermined path in the direction of the destination node.

Hence, the transmission of data packets in the communication networkcomprising synchronized nodes via a predetermined path is improved inthat high-priority data packets on this predetermined path are notdelayed by low-priority data packets. To this end, the secondhigh-priority data packets are fed into the predetermined path of thecommunication network in a specific manner. Here, the additional secondhigh-priority data packets are fed in at the nodes along thepredetermined path that send no or fewer high-priority data packets,particularly realtime data, than the other nodes. This minimizes theend-to-end delay and the jitter in the high-priority data packets,particularly in the control and regulatory data. This provides a higherquality of service in the communication network.

A further advantage is that in the respective node it is not necessaryto change the scheduling for selecting the next data packet to be sent,particularly based on the strict priority method. Hence, unlike thosemethods in which all the transmission instants are scheduled, such as inthe case of PROFINET IRT (Asynchronous Realtime), the present method ismuch easier to configure and imposes lower requirements on the hardwareof the respective node. Furthermore, the present approach is compatiblewith other nodes of the communication network that do not support thepresent expansion given reduced performance.

As already stated above, the additional feeding of short high-prioritydata packets or packets to all those nodes of the path of thecommunication network that transmit no or fewer dedicated high-prioritydata packets than the other nodes of this path is advantageous. Thisprevents low-priority long data packets from being transmitted at thebeginning of the respective time window and high-priority data packetsarriving from adjacent nodes being blocked.

By way of example, the communication network is an Ethernet,particularly a PROFINET. The nodes are synchronized, i.e., they all havethe same system time. In addition, the synchronized nodes feed the datapackets into the predetermined path in sync, i.e., at predeterminedidentical instants. The source node is the source of the firsthigh-priority data packet, the destination node is the destination ofthe first high-priority data packet and the at least one intermediatenode is coupled in the predetermined path between the source node andthe destination node. The respective buffer store is in the form of aRAM store (RAM; Random Access Memory) or in the form of an EEPROM store(Electrical Erasable Programmable Read-Only Memory), for example.

The example below illustrates the operation of the present method. Forthe communication network of this example, it is assumed that all thecontrol and regulatory data are present at the beginning of the timewindow and that they can be marked with a higher priority than otherdata packets, such as via ULAN tagging, and can therefore be treated ashigh-priority data packets. Furthermore, it is assumed that thehigh-priority data packets with the control and regulatory data aretransmitted in short Ethernet packets having a minimum packet length of64 bytes or in slightly longer packets. In the case of 100 Mbit/sEthernet (Fast Ethernet), the transmission period for a short datapacket taking account of the preamble (7 bytes), which precedes thepacket, and the start-of-frame delimiter (1 byte) is around 6 μs.

By contrast, an Ethernet packet having a maximum length has atransmission period of approximately 120 μs. Between two successive datapackets, it is necessary to wait for a time for the interframe gapcorresponding to 12 bytes. The time for the interframe gap relates to aprescribed minimum interval of time between two data packets that are tobe fed in at a node of the predetermined path. In this case, theinterframe gap time corresponds to approximately 1 μs. The propagationspeed of Ethernet packets via twisted copper lines is approximately200,000 km/s. The resultant signal propagation time on a link with amaximum length of 100 m is therefore 500 ns.

In this example, three adjacent nodes of a communication path areconsidered. A left-hand node, in this case the destination node, isconnected via a link to a middle node, in this case the intermediatenode, which in turn has a direct link to a right-hand node, in this casethe source node. It is assumed that the middle node (intermediate node)wishes to send a low-priority long data packet and the right-hand nodewishes to send a high-priority short data packet to the left-hand node(destination node). Both nodes send the respective packet at thebeginning of the time window to their respective left-hand adjacentnode. At the middle node, the high-priority data packet arriving fromthe right-hand node would conventionally need to wait until the longlow-priority data packet has been transmitted completely. On account ofgreatly different transmission periods of 120 μs in comparison with 6μs, this would mean significant jitter for the high-priority data packetat the middle node. This effect would accordingly accumulate if therewere further intermediate nodes between the left-hand and middle nodes.To overcome this problem, the invention involves the additional secondhigh-priority data packet being fed in at the middle node with thedestination of the left-hand node. This second high-priority data packetmay be designed as a pure dummy data packet without meaningful packetcontent or can be produced by segmenting a large low-priority datapacket. In the latter case, the segments are brought together again atthe destination node or an intermediate node along the path.

In accordance with the invention, however, the middle and right-handnodes send a high-priority data packet in the direction of the left-handnode (destination node) at the beginning of the time window. Thelow-priority long packet that exists at the middle node is buffer-storedon account of the lower priority. The interframe gap means that themiddle node must wait 1 μs after the transmission of the high-prioritypacket before the second high-priority data packet can be sent. Withinthis waiting time the high-priority data packet has already beenreceived completely from the adjacent right-hand node with thepropagation delay of no more than 500 ns via the link. Therefore, thehigh-priority data packet received from the right-hand node is selectedas the next data packet to be sent at the middle nodes and thelow-priority data packet continues to be buffer-stored. As a result, incontrast to the conventional scenario, the high-priority data packettransmitted by the right-hand node does not experience any waiting timeat the intermediate node but rather can be immediately forwarded by theintermediate node. Consequently, the end-to-end delays and the jitterare minimized.

In one embodiment, each of the intermediate nodes whose first bufferstore is empty at the particular instant and whose second buffer storeis filled with at least one low-priority data packet at the particularinstant generates the second high-priority data packet and feeds it intothe predetermined path in the direction of the destination node.

Advantageously, each intermediate node that does not buffer ahigh-priority data packet but buffers at least one low-priority datapacket therefore feeds a second and hence additional high-priority datapacket into the predetermined path. Consequently, the respectiveintermediate node does not transmit the buffered low-priority datapacket when the source node sends a high-priority data packet.Therefore, low-priority data packets are buffer-stored and not sent,which means that they cannot block the high-priority data packettransmitted by the source node.

In a further embodiment, the length of the second high-priority datapacket is set based on the length of the first high-priority datapacket. By setting the length of the second high-priority data packetbased on the length of the first high-priority data packet, the waitingtime that is set at the respective intermediate node for the firsthigh-priority data packet is advantageously set.

In a further embodiment, the length of the second high-priority datapacket is set based on maximum length of the low-priority data packets.The maximum length of the low-priority data packets prescribes themaximum delay for the first high-priority data packets. Consequently,this maximum length of the low-priority data packets can advantageouslybe taken as a basis for setting the length of the second high-prioritydata packet.

In a further embodiment, the nodes of the communication network aresynchronized via a time-division multiplexing method, where theparticular instant used is the beginning of a particular time window ofthe time-division multiplexing method. The time-division multiplexingmethod stipulates the particular instant for sending the data packets.

In a further embodiment, the time-division multiplexing method providesfirst time windows for an isochronous realtime service, second timewindows for a nonisochronous realtime service and third time windows fora nonrealtime service. In this case, the particular instant used is thebeginning of the second time window or the beginning of the third timewindow. Hence, the present method can be used for the aforementionedrealtime traffic (RT) and normal traffic (NRT).

In a further embodiment, the high-priority and low-priority data packetsare forwarded on the predetermined path in the second time window and inthe third time window on the basis of priorities associated with thedata packets.

In a further embodiment, the communication network is an Ethernetnetwork, particularly a PROFINET network.

In a further embodiment, the high-priority data packets have a firstmaximum data packet length and the low-priority data packets have asecond maximum data packet length. In this case, the second maximum datapacket length is greater than the first maximum data packet length.

In a further embodiment, the second high-priority data packet isgenerated by segmentation of a low-priority data packet stored in thesecond buffer store. This embodiment provides a simple way of generatingthe second high-priority data packet. In addition, this also transmitsmeaningful data as second high-priority data packets via thepredetermined path. The segments are then reassembled at the destinationnode or an intermediate node that is superordinate to the destinationnode.

In a further embodiment, the second high-priority data packet isgenerated as a dummy data packet. The dummy data packet has nomeaningful data in its useful data field, in particular. The use ofdummy data packets as second high-priority data packets is a form thatis very simple to implement.

In a further embodiment, if the propagation time for a data packetbetween two nodes of the predetermined path is shorter than a prescribedminimum interval of time between two data packets that are to be fed inat a node of the predetermined path, then a header of a data packetarriving and not yet completely received at the intermediate node isevaluated. In this case, the evaluated header is taken as a basis for asecond high-priority data packet to be generated by the intermediatenode and fed into the predetermined path. Alternatively, the arrivingdata packet is received completely and then fed by the intermediate nodeinto the predetermined data path again.

In a further embodiment, if the propagation time for a data packetbetween two nodes, of the predetermined path is shorter than aprescribed minimum interval of time between two data packets that are tobe fed in at a node of the predetermined path, then exclusivelyhigh-priority data packets are fed from the intermediate nodes into thepredetermined path.

The last two embodiments above are particularly suited to communicationnetworks with higher bit rates, e.g., for a gigabit Ethernet, becausethe latter may involve the interframe gap being shorter than the signalpropagation time on the link.

It is also an object of the invention to provide a computer programproduct that prompts the performance of the method as explained above ona program-controlled device.

A computer program product, such as a computer program means, can beprovided or delivered, for example, as a storage medium, such as amemory card, USB stick, CD-ROM, DVD, or else in the form of adownloadable file from a server in a network. This can be effected in awireless communication network, for example, by transmitting anappropriate file with the computer program product or the computerprogram means.

It is also an object of the invention to provide a data storage mediumhaving a stored computer program with commands that prompts theperformance of the method as explained above on a program-controlleddevice.

In addition, it is an object of the invention to provide a communicationnetwork comprising synchronized nodes for transmitting data packets viaa predetermined path in the communication network, where thesynchronized nodes of the predetermined path comprise a source node, adestination node and at least one intermediate node, feed data packetsinto the predetermined path in synchronized form and each have a firstbuffer store for buffer-storing high-priority data packets and a secondbuffer store for buffer-storing low-priority data packets, and whereeach of the intermediate nodes whose first buffer store is empty at aparticular instant at which the source node feeds a first high-prioritydata packet into the predetermined path in the direction of thedestination node is set up to generate a second high-priority datapacket and to feed it into the predetermined path in the direction ofthe destination node.

Other objects and features of the present invention will become apparentfrom the following detailed description considered in conjunction withthe accompanying drawings. It is to be understood, however, that thedrawings are designed solely for purposes of illustration and not as adefinition of the limits of the invention, for which reference should bemade to the appended claims. It should be further understood that thedrawings are not necessarily drawn to scale and that, unless otherwiseindicated, they are merely intended to conceptually illustrate thestructures and procedures described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The properties, features and advantages of this invention that aredescribed above and also the manner in which they are achieved willbecome clearer and more distinctly comprehensible in conjunction withthe description below of the exemplary embodiments that are explained inmore detail in conjunction with the drawings, in which:

FIG. 1 shows a schematic diagram of a network topology for acommunication network;

FIG. 2 shows a schematic diagram for the conventional transmission ofdata packets via the communication network of FIG. 1;

FIG. 3 shows a flowchart for an exemplary embodiment of a method fortransmitting data packets in a communication network comprisingsynchronized nodes;

FIG. 4 shows the schematic diagram of the network topology of thecommunication network of FIG. 1; and

FIG. 5 shows a schematic diagram for the inventive transmission of datapackets via the communication network of FIG. 3.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

In the figures, elements that are the same or that have the samefunction have been provided with the same reference symbols unlessstated otherwise.

FIG. 3 shows a flowchart for an exemplary embodiment of a method fortransmitting data packets P1-P4 in a communication network N comprisingsynchronized nodes A-D via a predetermined path P in the communicationnetwork N. In this regard, FIG. 4 shows a schematic diagram of thenetwork topology of such a communication network N and FIG. 5 shows aschematic diagram for the transmission of the data packets P1-P4 via thecommunication network 1 in accordance with the invention. Thesynchronized nodes A, B, C, D of the predetermined path P comprise asource node D, a destination node A and two intermediate nodes B, Carranged in between them. The nodes A-D are set up to feed the datapackets P1-P4 into the predetermined path P in synchronized form. Therespective node A-D has a first buffer store for buffer-storinghigh-priority data packets P1, P3, P4 and a second buffer store forbuffer-storing low-priority data packets P2 (not shown).

In step 301, the source node D feeds a high-priority data packet P3 intothe predetermined path P in the direction of the destination node A. Instep 302, each of the intermediate nodes B, C whose first buffer storeis empty at the particular instant feeds a second high-priority datapacket P4 into the predetermined path P in the direction of thedestination node A. In the example in FIG. 5, this applies only to theintermediate node C, because the intermediate node B is itself alreadyfeeding in a first high-priority data packet P1. The nodes A, B, C, Dare synchronized and feed synchronized data packets P1-P4 into the pathP. As a result, steps 301, 302 are performed simultaneously, i.e., atthe particular instant.

At this particular instant, each of the intermediate nodes C, inparticular, feeds a second high-priority data packet P3 into thepredetermined path P whose first buffer store is empty at the particularinstant and whose second buffer store is filled with at least onelow-priority data packet P2 at the particular instant. The length of thesecond high-priority data packet P4 is preferably set based on thelength of the first high-priority data packet P3 and/or based on amaximum length of the low-priority data packets P2.

The nodes A, B, C, D are synchronized via a time-division multiplexingmethod, the particular instant used being the beginning of a particulartime window of the time-division multiplexing method. By way of example,the time-division multiplexing method provides first time windows for anisochronous realtime service, second time windows for a nonisochronousrealtime service and third time windows for a nonrealtime service. Theparticular instant used in each case can be the beginning of the secondtime window or the beginning of the third time window.

The high-priority and low-priority data packets P1, P2, P3, P4 areforwarded in the second time window and the third time window based onpriorities associated with the data packets P1, P2, P3, P4 and based onstatic multiplexing on the predetermined path P. The respective secondhigh-priority data packet P4, which can also be called an additionalhigh-priority data packet, is generated by segmenting a low-prioritydata packet P2 stored in the second buffer store, for example.Alternatively, the second high-priority data packet P4 may also bedesigned as a dummy data packet without meaningful data in its usefuldata field.

If the propagation time for a data packet P1-P4 between two nodes A-D ofthe predetermined path P is shorter than a prescribed minimum intervalof time between two data packets P1-P4 that are to be fed in at a nodeA-D of the predetermined path P, a header of a data packet P3 arrivingand not yet completely received at the intermediate node C is evaluated.In addition, the evaluated header is taken as a basis for a secondhigh-priority data packet P4 to be generated by the intermediate node Cand fed into the predetermined path P. Alternatively, the arriving datapacket P3 can be received completely and then fed into the predeterminedpath P again by the intermediate node C.

Alternatively, for the above case in which the propagation time for thedata packet between two nodes of the predetermined path P is shorterthan a prescribed minimum interval of time between two data packetsP1-P4 that are to be fed in at the node of the predetermined path P,exclusively high-priority data packets can be fed into the predeterminedpath P from the intermediate node C.

As stated above, FIG. 4 shows the schematic diagram of the networktopology of the communication network N for performing the method ofFIG. 3. In this regard, FIG. 5 shows a schematic diagram for theinventive transmission of the data packets P1-P4 via the communicationnetwork N. Here, FIG. 5 visualizes the message flow of the packets.P1-P4. In this case, an additional high-priority packet P4, which hasthe destination node A as a destination, is fed in at the node C. Thehigher priority of the additional high-priority data packet P4 over thelow-priority data packet P2 means that the data packet P4 is sent at thebeginning of the cycle. Following the transmission of this high-prioritydata packet P4, the next data packet for transmission is selected afterthe interframe gap has elapsed. At this instant, both the low-prioritydata packet P2 and the high-priority data packet P3 that has alreadybeen received from the adjacent node D are available for selection. Thisis possible because in the case of 100 Mbit/s Ethernet the propagationdelay of the signals on the link is shorter than the duration of theinterframe gap. Therefore, the high-priority data packet P3 is thenforwarded immediately by the node C and arrives at the destination nodeA with minimized end-to-end delay and jitter.

The approach described is not limited to PROFINET but can be applied toall other Ethernet solutions that define time cycles by synchronizationof the nodes or stations and use prioritization of packets. A furtherexample of this is Ethernet POWERLINK.

In addition, the approach described can also be applied to data packetsin a plurality of priority classes, the low-priority data packets beingassociated with a lower or the lowest priority class and thehigh-priority data packets being associated with a high or the highestpriority class.

Although the invention has been illustrated and described in more detailby the preferred exemplary embodiment, the invention is not limited bythe disclosed examples and it is possible for other variations to bederived therefrom by a person skilled in the art without departing fromthe scope of protection of the invention.

Thus, while there have been shown, described and pointed out fundamentalnovel features of the invention as applied to a preferred embodimentthereof, it will be understood that various omissions and substitutionsand changes in the form and details of the devices illustrated, and intheir operation, may be made by those skilled in the art withoutdeparting from the spirit of the invention. For example, it is expresslyintended that all combinations of those elements and/or method stepswhich perform substantially the same function in substantially the sameway to achieve the same results are within the scope of the invention.Moreover, it should be recognized that structures and/or elements and/ormethod steps shown and/or described in connection with any disclosedform or embodiment of the invention may be incorporated in any otherdisclosed or described or suggested form or embodiment as a generalmatter of design choice. It is the intention, therefore, to be limitedonly as indicated by the scope of the claims appended hereto.

The invention claimed is:
 1. A method for transmitting data packets in acommunication network comprising synchronized nodes via a predeterminedpath in the communication network, wherein the synchronized nodes of thepredetermined path comprise a source node, a destination node and atleast one intermediate node, said synchronized nodes feedingsynchronized data packets into the predetermined path and each having afirst buffer store for buffer-storing high-priority data packetscomprising control and regulatory data and a second buffer store forbuffer-storing low-priority data packets, the method comprising:generating, by the at least one intermediate nodes, a secondhigh-priority data packet when said at least one intermediate nodes hasan empty first buffer store at a particular instant at which the sourcenode feeds a first high-priority data packet comprising control andregulatory data into the predetermined path toward the destination node;and feeding the generated second high-priority data packet into thepredetermined path toward the destination node.
 2. The method as claimedin claim 1, wherein the at least one intermediate node having the emptyfirst buffer store, at the particular instant and having a second bufferstore filled with at least one low-priority data packet comprisingcontrol and regulatory data at the particular instant, generates thesecond high-priority data packet and feeds the generated secondhigh-priority data packet into the predetermined path toward thedestination node.
 3. The method as claimed in claim 2, wherein a lengthof the second high-priority data packet is set based on a length of thefirst high-priority data packet comprising control and regulatory data.4. The method as claimed in claim 2, wherein a length of the secondhigh-priority data packet is set based on a maximum length of thelow-priority data packets.
 5. The method as claimed in claim 1, whereina length of the second high-priority data packet is set based on alength of the first high-priority data packet comprising control andregulatory data.
 6. The method as claimed in claim 5, wherein the lengthof the second high-priority data packet is set based on a maximum lengthof the low-priority data packets.
 7. The method as claimed in claim 1,wherein a length of the second high-priority data packet is set based ona maximum length of the low-priority data packets.
 8. The method asclaimed in claim 1, wherein the synchronized nodes of the communicationnetwork are synchronized via a time-division multiplexing method, andwherein the particular instant utilized is a beginning of a particulartime window of the time-division multiplexing method.
 9. The method asclaimed in claim 8, wherein the time-division multiplexing methodprovides first time windows for an isochronous realtime service, secondtime windows for a nonisochronous realtime service and third timewindows for a nonrealtime service, and wherein the particular instantutilized is a beginning of the second time window or a beginning of thethird time window.
 10. The method as claimed in claim 9, wherein thehigh-priority comprising control and regulatory data and low-prioritydata packets are forwarded in the second time window and in the thirdtime window based on priorities associated with the high-prioritycomprising control and regulatory data and low-priority data packets.11. The method as claimed in claim 1, wherein the communication networkcomprises an Ethernet network.
 12. The method as claimed in claim 11,wherein the Ethernet network comprises a PROFINET network.
 13. Themethod as claimed in claim 1, wherein the high-priority data packetscomprising control and regulatory data have a first maximum data packetlength and the low-priority data packets have a second maximum datapacket length which is greater than the first maximum data packetlength.
 14. The method as claimed in claim 1, wherein the secondhigh-priority data packet is generated by segmentation of a low-prioritydata packet stored in the second buffer store.
 15. The method as claimedin claim 1, wherein the second high-priority data packet is generated asa dummy data packet, particularly without useful data.
 16. The method asclaimed in claim 1, wherein the dummy data packet is devoid of usefuldata.
 17. The method as claimed in claim 1, wherein if a propagationtime for a data packet between two nodes of the synchronized nodes ofthe predetermined path is shorter than a prescribed minimum interval oftime between two data packets of the synchronized data packets that areto be fed in at a node of the predetermined path, then a header of adata packet arriving and not yet completely received at the intermediatenode is evaluated, and wherein the evaluated header is taken as a basisfor one of (i) the second high-priority data packet to be generated bythe intermediate node and fed into the predetermined path and (ii) anarriving data packet to be received completely and then re-fed by theintermediate node into the predetermined data path.
 18. The method asclaimed in claim 1, wherein if a propagation time for a data packetbetween two nodes of the synchronized nodes of the predetermined path isshorter than a prescribed minimum interval of time between two datapackets of the synchronized data packets that are to be fed in at a nodeof the predetermined path, then exclusively high-priority data packetscomprising control and regulatory data are fed from the intermediatenodes into the predetermined path.
 19. A non-transitory computer programproduct encoded with a computer program, which when executed on aprogram-controlled device, causes performance of a method comprising:generating, by at least one intermediate nodes, a second high-prioritydata packet when said at least one intermediate nodes has an empty firstbuffer store at a particular instant at which a source node feeds afirst high-priority data packet comprising control and regulatory datainto a predetermined path toward a destination node; and feeding thegenerated second high-priority data packet into the predetermined pathtoward the destination node.
 20. A communication network comprising:synchronized nodes for transmitting data packets via a predeterminedpath in the communication network; wherein the synchronized nodes of thepredetermined path comprise a source node, a destination node and atleast one intermediate node, feed data packets into the predeterminedpath in synchronized form and each of the synchronized nodes include afirst buffer store for buffer-storing high-priority data packetscomprising control and regulatory data and a second buffer store forbuffer-storing low-priority data packets; and wherein each of theintermediate nodes having an empty first buffer store at a particularinstant at which the source node feeds a first high-priority data packetcomprising control and regulatory data into the predetermined path inthe direction of the destination node is configured to generate a secondhigh-priority data packet and to feed the generated second high-prioritydata packet into the predetermined path toward the destination node.